Corrosion Inhibition of Mild Steel in Hydrochloric Acid Solution using Methanolic Extracts of Elsholtzia communis and Spilanthes acmella as Green Inhibitors

The corrosion inhibition effect of methanolic extract of Elsholtzia communis inflorescence (ECI) and Spilanthes acmella (SA) towards the corrosion of mild steel in 1 N HCl solution was examined by means of weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The corrosion rate was found to decrease with increasing ECI and SA concentration up to 0.5 g/L at 27 ºC. The temperature effect on inhibition effect of plant extracts has also been discussed. Nyquist plots showed that methanolic extract of ECI yielded the best inhibition efficiency. The adsorption of inhibitor on the mild steel surface was found to obey the Langmuir adsorption isotherm through which various thermodynamic parameters were calculated and discussed. Surface morphology of the mild steel after exposing to test solutions in absence and presence of inhibitor were investigated by scanning electron microscope (SEM), which show that the corrosion of mild steel is retarded to great extent by ECI and SA extracts. The phytochemicals screening were performed by gas chromatography-mass spectroscopy (GC-MS) study based on this study effective inhibitor molecules and inhibitive mechanism can be established. The GC-MS and FT-IR studies of ECI and SA extracts indicated that the adsorption centre in green inhibitor probably due to presence of β-retinoid and its derivatives in ECI and SA extracts showed that the adsorption centre due to presence of fatty acid derivatives.